ROME, Aug 24 (Reuters) - Italy's maritime search and rescue service saved 3,500 migrants and found 19 corpses in the Mediterranean since Friday as thousands attempted to cross to Europe by boat over the weekend, the Italian navy said.

Calmer summer seas have led more people to make the perilous crossing this year from North Africa, where a breakdown of order in Libya has been exploited by human traffickers, pushing the number of arrivals into Italy since January past 100,000.

The Italian ship Sirio recovered 18 corpses and 73 survivors from a raft, the navy said on Twitter on Sunday, after a frigate picked up one corpse along with 1372 survivors on Friday night.

The deaths were reported shortly after a boat carrying migrants sank off the Libyan coast on Friday. The Libyan coast guard originally estimated the boat had held 150-200 people, but an official said on Sunday further checks showed it was bigger than first thought, and more than 250 migrants may have died.

The Mare Nostrum search and rescue mission began after a shipwreck near Italy's coast killed 366 people last October. The UN refugee agency said around 500 migrants had died in the Mediterranean between January and July this year.

The mission costs around 9 million euros ($11.92 million) a month and has sparked fierce debate in Italy, which slipped back into recession in the second quarter after years of stagnation.

The flood of migrants has helped revive support for Italy's anti-immigration Northern League party, whose leader Matteo Salvini is an outspoken critic of Mare Nostrum. Salvini wrote "Stop the Invasion" on his Facebook page on Sunday.

Interior minister Angelino Alfano said in an interview with the Corriere della Sera newspaper on Sunday that Mare Nostrum was intended to be a temporary measure which could not continue until the second anniversary of the October shipwreck, and voiced concern over the Northern League's vociferous opposition.

"Either Europe takes responsibility or Italy will have to make its own decisions. Sadly, Salvini's words show that in Italy an ugly extreme right wing is being born," Corriere quoted Alfano as saying.

EU Home Affairs Commissioner Cecilia Malmstrom said in a statement later on Sunday that she would meet Alfano in Brussels next Wednesday "to better define priorities and provide assistance".

At the frontier between Europe and Africa, Italy has long attracted sea-borne migrants, but the number of arrivals this year is already above a previous record of just over 60,000 for all of 2011, when the Arab Spring uprisings fuelled migration.

Italian Prime Minister Matteo Renzi has called on the European Union to take responsibility for rescuing migrants by investing in border control agency Frontex, and on the United Nations to intervene in Libya to manage the flows of refugees. (1 US dollar = 0.7552 euro) (Reporting by Isla Binnie; Editing by Raissa Kasolowsky and Stephen Powell)

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